1. Field of the Invention
The present invention relates to permanent air filters, and is more particularly concerned with an air filter which includes a throwaway cover protion therein.
2. Description of the Prior Art
It is known to make a filter by sandwiching a glass fiber batt and at least one stamped metal sheet disposed on the side of impact of the moving air upon the fibreglass, and preferredly a metal sheet in each side of the fibreglass to hold the parts together. Such a filter is commonly used to remove particulate matter from air used in heating and air conditioning systems. Such a filter has several disadvantages. First, it is relatively flexible and thus easily distorted upon insertion into the filter holder. Second, the dust accumulates only on one side, but since the frame is usually card stock, the filter cannot be washed off and reused easily as the fibreglass is not cleanable and the card stock becomes water logged.
In general, air filters of the prior art have a porous filter medium of substantial thickness comprising a fluffy mass of glass fibers generally bonded at the outside edges where they touch one another by means of a suitable adhesive to yield a batt. A complementary frame is provided to support the filter medium layer.
An example of an early form of air filter embodying glass fiber filter medium is found in U.S. Pat. No. 2,677,436 showing a frame consisting of I-beams and skeletonized wire network panels covering the opposite faces of the filter layer.
The advantage of leaving at least one face of the filter layer for substantially free entry of air is shown in U.S. Pat. No. 3,023,839 wherein both faces are relatively unimpeded.
The design of the air filter has remained substantially unchanged since its early introduction. Such structure comprises the filter element formed of a core of glass fibers bound together by small particles of a resinous binder and often coated with a thin transparent film of a viscous non-volatile oil, to retain airborne particles impelled against the fibers by the air movement. The filter element is retained between two closely perforated sheets of brass metal commonly known and available as bottle cap scrap. The filter and the pair of perforated confining brass sheets are held together within an inwardly facing U-channel of a hollow frame of sturdy but inexpensive fiberboard, often decorated and reinforced by an overlay of imprinted paper tape. The side pieces of fiberboard are glued with an adhesive such as a hot melt or pressure-sensitive adhesive, or stapled together at their ends to form the corners of the frame. This type of filter is readily available today and is used in millions of homes as a throwaway filter which is changed every three to six months. People however have changed their buying habits for several reasons. The era of throwaway items is declining as people realize the necessity to conserve raw materials, not only in the U.S. but worldwide. In addition, many people psychologically would rather buy one good product to carry out a service, which product can be renewed for further use such as the filters of this invention.